Photoelectric apparatus for generating musical tones



M. CLARK, JR 2,946,253

PHOTOELECTRIC APPARATUS FOR GENERATING MUSICAL ToNEs July 26, l1960 7Sheets-Sheet 1 Filed 001'.. 3l, 1955 @d .J 5 )k Rl Vl L y. 5 .A EL 0M PJ I.. N A W. W l. .mmm s w A M .Q M w z R awm am. d@ )m July 26, 1960 M.CLARK, JR 2,946,253

PHOTOELECTRIC APPARATUS FOR GENERATING MUSICAL TUNES med on. s1, 1955 7Sheets-Sheet 2 INVEN TOR. /Vfz Wai (244% ./P.

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July 26, 1960 PHOTOELECTRIC APPARATUS FOR GENERATING MUSICAL. TONESFiled Oct. 31, 1955 7 Sheets-Sheet 3 INVEN TOR. /VH m15 fue@ ./P.

M. CLARK, JR 2,946,253

PHOTOELECTRIC APPARATUS FOR GENERATINC MUSICAL TONES July 26, 1960 7Sheets-Sheet 4 Filed Oct. 3l, 1955 uvVENToR. /Vfz m4; 624m; Je

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July 26, 1960 7 Sheets-Sheet 5 July 26, 1960 M. CLARK, JR 2,946,253

PHOTOELECTRIC APPARATUS FOR GENERATING MUSICAL TONES Filed Oct. 5l, 19557 Sheets-Sheet 6 F/GJ/ F16. /0 INVENToR.

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BYa- M15 Y M. CLARK, JR 2,946,253

PHoToELEcTRIc APPARATUS Foa GENERATING MUSICAL ToNEs July 26, 1960 '7Sheets-Sheet 7 Filed Oct. 5l. 1955 INVENTOR. /Viz ma: 62443K, ./42

Unite States vlI-,IOIOELECTRIC APPARATUS FOR 'GENERATING MUSICAL TONES.Melville Clark, an., Boston, Mass. (Dept. of chemical Engineering,Massachusetts Institute of Technology, Cambridge S9, Mass.)

Filed Oeh-31, '1955, Ser. No. '543,865

6 Claims. (Cl. Ski- 1.18)

This invention relatesto electrical musical instruments; and inparticular to improved means in such instruments ,for producing complextonalities simulatingorchestral music; .to `improvetnerds in opticalsystemsfor photoelec- :tric musical instruments, preferably of therotatingdisc type; and to improvements in `driving mechanisms for:rotating the `modulation discs in such instruments.

An object of this invention is to provide an improved electrical`musical instrument for .simulating .the tones of orchestral and otherinstruments more faithfully than has been .possible heretofore.

Another Yobject is to provide an electrical musical instrumentfor-simulating the composite tonalities pro- :duced by groups oforchestral or other instruments, inc luding entire symphony orchestrasor orchestral sections.

Another object is to provide an electrical musical `instrument havinggreat musical resources, particularly with respect to the number andvariety of complex tonalities that may be produced, which issuliiciently simple and convenient to operate kthat `auch resources canAbe effectively utilized by a musician of reasonable prociency j lAnother object is to provide a musical instrument on which a person withmodest training and ability can produce tones which kcan be produced onconventional instruments only after long practice by able musicians.

Another object is `to provide an eleetricalmusical instrument ,having astop or timbre-control system Yfor .simulating n plurality ofv differentinstruments simultavneousiy, in which the stop adjustments are additiveso `that an adjustment for'simulating one instrument Vcan be I Imade"without disturbing previously-made adjustments for simulating otherinstruments, and Without robbing vthe tones representing such otherinstruments.

Another object is to provide an electrical musical ,-instrument in whichthe timbre or tone color may vary as `a function of pitch. v

.Another object is to provide an improved musical instrument Vthat maybe constructed lin a variety of sizes,

'ranging :from small inexpensive accordion-size portable instrumentsShaving limited musical resources 4to large console instruments forsimulating organ and r-symphonic im'usic.

Another object is to provide `an improved electrical lmusical instrumentthat is :exceptionally compact, light and 'economical lto manufacture,considering its vmusical cap abilities.

Another object is to provide an improved electrical `musical instrumentthat 4is rugged, that does not require tuning, and that requires aminimum amount of service and maintenance.

-Another object is `to provide a photoelectric musical instrument havingan improvedoptical :system that permits a compact and economicalconstruction, that is easily llinked 'to 'the keys fof piano and organvtype ykeyboards by `'simplemechanical linkages,=and that consumes butIa small amount of electric power.

l 2,946,253 1C@ Patented July ze, `leso Another object is'to provide animproved photoelectric musical instrument that is substantially freefrom ditliculties due to the presence of dust and other foreignsubstances, and is unalfected by temperature and humidity changes.

Another object is to provide a musical instrument hav- `ing anexceptionally wide dynamic range with a large signal-to-noise ratio.

Still another object -is to provide a rotating-disc type of musicalvinstrument having an `improved Idriving mechanismfor rotating thediscs. A

Other objects land advantages of this invention will Iappear as `thedescription proceeds. f

Briefly stated, in accordance with one aspect of `this l5 invention,signals representing diiferent basic complex tonalities are generatedsimultaneously and `are combined to produce a composite musical tone.Preferably, each basic tonality simulates a different orchestrallinstrument or a group of instruments, and the composite tone `maysimulate lan entire orchestra. The timbre or character of the compositetone is controlled by a stop lor timbre-control system for adjusting therelative amplitudes ofthe -basic signals. For example, a signalsimulating the ltonality Yof a violin or orchestral string section maybe controlled by a single stop adjustment mechanism, so that themusician can provide more -or less :of the violin tonality by changing asingle stop adjustment. The stop adjustments can be changedindiyidually. 4

This arrangement has-many advantages over harmonic synthesis methods forcomplex tone generation often used V`in electric organs; especially withrespect to playing `Vconvenience and the demands made upon thecapabilities lof the musician, which are limited even in vthe -case ofthe most yaccomplished musicians by limitations of the 4human body.Since instruments embodying principles of this `invention have stopsystems that can be adjusted much ,more .quickly and conveniently thanis the -case with instruments using harmonic synthesis .,methods,- stopor timbre changes can be made with much less interruption Yof themusical composition. The lstop adjustments yare additive, so that theadjustment controlling tones ysimulating one instrument or group ofinstruments can be changed Without affecting previously-made stopadjustments or the tones simulating other instruments Yfor which thestops have previously been set. Furthermore, the selection of unpleasantor undesirable'tone `combinations is automatically made dilcult.

.YA different basic tone signal can be provided-to simu- Ilateeachindividual instrument of an orchestra or orchestral section. To alimited extent this may be `desirable to provide facilities forsimulating solo renditions. However, the structure and playing of theelectrical musical instrument can be greatly simplified by providingbasic vsignals that simulate groups or families yof instruments.According to another aspect of this invention, the orchesr4tralinstruments are grouped into families in which each family consists of aplurality of instruments having tonalities which are similar in qualityor timbre, but which ydilfer chiefly in register. A basic signal isprovided with a'timbre representative of a family of instruments, suchas the string family. This basic signal closelyapproximates the timbreof any instrument with` in the family. The musician can produce more orless 5 of the `string-section tonality by changing a single `stopadjustment. With this arrangement, all of the undamped or non percussive1tojnes of a symphony orchestra can be produced with as few as six basictimbres.

It should be realized, however, that certain principles Yof thisinvention can be used in instruments using harmonic synthesis methods ofcomplex tone generation.

When harmonic synthesis is employed, a signal may be provided having thefundamental frequency of a selected pitch, and other signals may beprovided having frequencies corresponding to different overtones of thesame pitch. The improved photoelectric tone generation apparatus .hereindescribed provides significant advantages 'in such a system-for example,the basic signals generated may be combined optically in a trulyadditive manner without the robbing difficulties often encountered inother electrical musical instruments. Also, properly pitched harmonicand non-harmonic overtones can be provided in a relatively simple andconvenient manner.

A modified harmonic synthesis system may be especially advantageous insmall, low-cost instruments. One signalmay be used to represent thefundamental, and one or more other signals may be used to representselected combinations of overtones, with or without a fundamentalfrequency component in each overtone signal.

In addition to the basic timbres or signals used to simulate theundamped tonalities of orchestral music, other signals may be providedif desired to simulate damped or percussive tones, and also to producenovel or unconventional tones not usually produced by presentlyknownorchestral instruments.

In accordance with another aspect of this invention, an improvedphotoelectric musical instrument is provided in which basic tones areproduced by the modulation of light beams, preferably by a plurality ofparallel coaxial rotative tone discs each carrying a plurality ofconcentric circular modulating tracks each having an opticaltransmittance that varies along the length of the track. These trackspreferably are of the variable-density type, althrough variable-arca orother types of modulating tracks may sometimes be used. In a preferredembodiment, there is a tone disc for each different pitch, and the discsare rotated at different constant speeds by driving mechanismshereinafter described. On each disc there is a light-modulating trackfor each basic timbre. Electric lamps are used as a light source orlight sources, and one or more photoelectric transducers are provided toconvert modulated light into electric signals.

Novel light-transmitting systems herein -described define a plurality oflight beam paths passing between the parallel discs and crossingrespective ones of the modulation tracks, so that a plurality ofmodulated light signals are provided to represent the diierent basictimbres of each pitch. The quality or timbre of a composite tone ispreferably controlled by adjusting the relative amounts of lighttransmitted through tracks representing dierent basic timbres.

The improved optical systems are Suiciently compact that the averagespacing between tone discs is equal to the average spacing between keysof a standard piano or organ-type keyboard, so that a simple andfast-acting keying system is made possible. In the improved opticalsystem, each electric lamp supplies light to a plurality of trackscarried -by diterent tone discs, so that the number of lamps required issmall, which is particularly advantageous in simplifying maintenance andin reducing the electric power consumption and the attendent produc-'ion of heat.

In 'accordance with still other aspects of this invention, a step-likearray of distribution mirrors is used to provide parallel light beamspassing through alternate ones of the spaces between the rotative tonediscs, and V-shaped mirrors positioned between the tone discs areemployed to split each of these beams into two parts passing in oppositedirections through tracks carried by adjacent ones of the discs. OtherV-shaped mirrors and a similar step-like array of mirrors may be used incollecting the modulated light transmitted by the modulation tracks.

Adverse eects of dust and the like are minimized by the use ofphotographically produced transparent optical apertures, and, ifdesired, by enclosing and sealing the optical system.

In accordance with still another aspect of this invention, -a pluralityof modulation tracks are provided to simulate the musical tones ofdifferent pitch that may be produced by an orchestral instrument orgroup of instruments. The modulation tracks for diEerent pitches aresimilar in that they simulate tones produced by the same instrument orgroup of instruments, but they differ in timbre lor harmonic content tosimulate the variations of tone color as a function of pitch that arefound in actual orchestral instruments.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings, and its scope willbe pointed out in the appended claims.

In the drawings:

Fig. 1 is a simplified schematic and circuit diagram of an electricalmusical instrument embodying principles of this invention;

Fig. 2 is a schematic plan view, partly in section, of a novel opticalsystem for the same musical instrument;

Fig. 3 is a section taken generally along the line 3 3 of Fig. 2;-

Fig. 4 is a detail showing one of the keying shutters of the sameinstrument;

Fig. 5 is a detail showing an alternative keying shutter;

Fig. 6 is a transverse section of a tone disc of the same musicalinstrument;

Fig. 7 is a schematic plan view illustrating a preferred drive mechanismfor -rotating the tone discs;

Fig. 8 is a section taken generally along the line 8-8 of Fig. 7;

Fig. 9 is a schematic plan view showing an alternative optical systemfor the improved musical instrument;-

Fig. l0 is a schematic plan view, partly in section, showing anotheralternative optical system for the improved musical instrument;

Fig. l1 is a section taken along the line 11--11 of Fig. 10; and

Fig. 12 is a schematic plan view, partly in section, showing stillvanother alternative optical system for the improved musical instrument.

Reference is now made to Fig. l of the drawing, which is a simpliedschematic and circuit diagram of the improved musical instrument,including one tone disc for producing one musical pitch of varioustimbres. Other tone discs are provided (as is shown in subsequentfigures of thisapplication) for producing other pitches; there being, ingeneral, one or more tone discs for each pitch. For example, aninstrument for simulating organ I nusic will generally cover a range ofsixty-one diterent pltches or semitones, and will have sixty-one or moretone discs, although in certain circumstances tones of two or moredifferent pitches may be placed upon each disc so that a smaller numberof discs may be used. A larger number of discs is employed when thenumber of diierent timbres or tonalities of each pitch, or the number ofkeyboards used in the instrument, is suiciently great that more than onetone `disc may more conveniently be used for each pitch.

The instrument illustrated in Fig. 1 has two standard piano ororgan-type keyboards, and is capable of producing three dierent timbresof each pitch. However, -a larger number of timbres may be provided byadding additional modulation tracks to each disc, or by increas- -ingthe number of discs, and ten or more different timbres of a given pitchmay easily be accommodated on a single .tone disc of reasonable size. n

The tone disc 1 is rotative about a shaft 2, and 1s driven at constantspeed by suitable means such as a motor 3 and a driving wheel 4. Tonedisc 1 carries three concentric .circular modulations tracks each havinga circular modulated section with an optical transmittance that variesalong its rlength in accordance with a different accepts 5 musicalArtone, preferably three different timbres of the same musicalpfitch.Thetra'cks may also `have unmodullated-opaque, 'for yexample-sectionsfor purposes hereinafter described.

Light 'is produced -by six electric lamps, identified in thetdrawing Ibyreference numerals 5, 6, 7, 8, 9 and 10. -There 'is also provided twophotoelectric transducers 11 "and 12, which preferably l.arephotomultipl-ier tubes, for 4converting modulated light yinto electricsignals.

An optical transmission system hereinafter described defines a-plurality of optical paths .between each of the y'lamps '5, 6 a'nd'7and the transducer 11. These paths cross modulated rsections of'respective ones of the modulation tracks carried by tone d isc 1, andare normally blocked by a Ykeying shutter 13. Shutter 13 has threeoptical :apertures las shown, and is mechanically linked 'to a playingkey l=14 in one keyboard of .the instrument. Key 14 may be a key vot :a:manual.keyboard, or it may be apedal of a -pedal clavier.

vWhen key l14 `is depressed,the apertures of shutter 13 aresimultaneously moved into alinement with optical paths .from lamps 5, 6and 7 that cross modulated sections 4of the .three modulation trackscarried by disc 1, so that .thesethree paths are simultaneouslyunblocked and 4modulated light of ,three different basic timbres ortonalikties reaches .transducer 11 when all three of lthe lamps 5, 6-and7 arelit. The amount oilight transmitted in each of Vthese threepathscan be adjusted in a manner herein- Aafter described, by adjusting therelative amounts of `electric current Yilowing through lamps 5, 6 and 7for example, to control the vrelative .intensities of the three tbasic-tonalities that make up a--composite timbre of the musical`toneproduced by the instrument.

loud-speakers 28 which convert 'the electric 'signals into sound Waves.

The composite timbre or tonality'produced Wheneither or both of the keys14 and 16 are depressed -is controlled by a stop system that preferablyrincludes means for individually adjusting the relative amounts Ao'felectric current supplied to the lamps,V 5, 6, 7, 8, 9 and '10.Alternating electric current is supplied to leads 29 and 30 from anysuitable source such as a commercial 60- cycle electric outlet.VConnections are `made to leads -239 and 3% for supplying electric powerto the Ypower supply 17 and to other power supplies, not shown, lfor theamplifiers and other electrical components of r-tl1e"musi`cal .A similaroptical ltransmission system deiines optical i ,paths between lamps 8,.9 .and 10 'and the transducer 12, whichpaths preferably cross the samemodulated sections of ythe tracks -carried by disc 1. These latter pathsare normally blocked by 1a shutter 15 which yhas three aper- Itures, asshown, and which is linked to a playing key 16 .in a .second manualkeyboard `or pedal clavier. The current supplied to lamps 8, 9 and 1dmay be adjusted .findividuallyso that a different composite timbreor'com- :bination of b'asic tonalities vis produced when key 16 is=depressed than is produced when key 14 is depressed.

Operating voltages Vfor Vthe photomultiplier ltransducers 11 A'and I2are :supplied by a power supply 17 through conventional resistance-typevoltage dividers as shown.

The Vanode or photornultiph'er 11 is 'connected to an ampliiier-ltand'supplies thereto an electric signal corre- :spondin-g to thecomposite Vmodulation `of the 'light refceived by `photomultiplier 11.The output of amplifier 13 .is vcorrnecte'dto a volume control 19,vwhich may be a 'resistan'celtype'voltage 'divider having a movable tap29 :linked to :aswell 'pedal 21 which may be operated l.to Acontrol theover-all volume 'of sound produced Vwhen key 14.is depressed. :Similarlythe ranode of photomultiplier 12 is connected to an amplifier 22 Whichsupplies an electric signal to a volume control 23 having an adjustabletap-24 linked to 'a Vsecond '.swellpe'dal 25which mayY beoperated'to'control Ythelover-all volume of sound produced When key 16:is depressed.

The .twovolume controls may be connected as shown tto any signalmodifiers r26 lthat it may be desired to in- '.corporate in itheinstrument. The signal 'modifiers lmay include 'reverberation devices,vibrato and tremolo producing apparatus, 'formant circuits, and thelike. VSuch Isi'gnal'modiers are known to'those skilled in the art, andmeednotbedescribed for an understanding of the present invention. Forfexatnple, a reverberation device which maybe employedis described onpages 522 and 523 of the v.book Elements of Sound Recording by `John G,Frayne and Halley Wolfe, published by John J'Wiley and l'iSons, Tric.,VvNew iYork, 1949. After passing through the signal .mo'diera thecomposite electric `'signal isv further amplied by an amplier 27 andsupplied to one or more instrument.

f Electric current is supplied to the lamps V5 through "10 by means of atransformerhaving a primary 31 :connected to leads 29' and 30, Iasshown. This transformer has 1a tapped secondary 32 connected to apluralitylofdistribution 'lines 33, 34 35 and 36, of which line 36is acommon line connected to one terminal of all lthe`^lan`ips 5 through 10.In this way 'different alternating voltages are supplied between line 36and each of the lines 33, 321, and 35. Preferably the secondary taps areso 'spaced as to provide equal lincrements 'in loudness betweensuccessive taps.

The second terminal of each lamp is rconnected tov afrespective one of aplurality of individually adjustable selector switches 37, 38, 39, 40,41 and 42, each ihaving three terminals connected to lrespective onesofthe -distribution lines 33, 34 and 3S and having a Afourth l-terminalthat is connected to none of the distribution "lines,

or alternatively is connectedrto line 36. By means -of these selectorswitches, the voltage supplied toeach lamp can be adjusted individuallyto Zero or to any oneof fthe voltage values appearing between line 36and the dS- tribution'lines 33, 34, and 35.

In this way the voltage supplied to each lamp, and hence the currentsupplied through ieach lamp and 'the amount of light produced vby thelamp, ycan be individually adjusted to control the relative amounts yoflight transmitted through VVdifferent ones of the optical paths.Selector switches 37 through 42 are parts of a stop system forcontrolling the composite timbre of musical .tones produced by theinstrument. 'Ihey may be mechanically connected to drawbars, dials orany `other convenient adjustment mechanism placed in position readilyaccessible tothe musician.

. The amount of hum produced by exciting the lamps with alternatingcurrent can `be made negligible and other advantages can be obtained byusing low kvoltage, incandescent lamps-6 volt lamps, for example-whichhave relatively heavy filaments and consequentlydo not 4change intemperature or brightness appreciably during an alternation of thesupply current. However, if desired, means may be provided for'supplying the .lamps with direct current or with high frequencyalternating current to eliminate any possibility of hum from thissource.

Since an optical path from eachlof the lamps r5, 6, and 7 crosses adifferent one of the three light-modulating tracks carried by disc 1,which tracks are modulated in accordance with dilerent timbres, thecomposite timbre of the tone produced when key 14 is depressed can Tbecontrolled by adjusting the switches 37, 38 and 39. In the same way, thecomposite timbre of the tone produced when key 16 is depressed can becontrolled by `adjusting the switches 4d, 41 and 42. The loudness ofeach of these tones is individually controlled by the twoswell pedals421 and 25, so that the musician can produceat will a great variety ofcomposite timbres from the three `basic timbres` represented by themodulation ofthe three lwithout departing from the broader princplesofthi`s.in

vention. The stop system may be modified, for example,

7 by the use of optical wedges and the like to adjust the relativeamounts of light transmitted through the different'optical paths insteadof using the selector switches 37 through 42 for adjusting the relativeamounts of current supplied to the various lamps.

According to another alternative, separate photoelectric transducers maybe provided to receive the light from each path, and the timbre of thecomposite tone can be controlled by adjusting the relative amplitudes ofthe different electric signals so produced. The swell pedals can alsooperate optical wedges for adjusting the amount of light reachingphotoelectric transducers 11 and 12 instead of adjusting the taps ofvoltage dividers 19 and 23. As still another alternative, other meansfor controlling the amplitudes of the electrical signals may be used .inplace of the resistance-type voltage dividers, such as variablecapacitances in feedback circuits of amplifiers 1S and 22.

yIf desired, the signals from amplifiers 18 and 22 may be combinedbefore such signals are supplied to the volume control operated by theswell pedal, in which case a single swell pedal may be used to controlthe overall amplitude of the composite signal, and hence to control theover-all loudness of the musical tone. Alternatively, signals may becombined by using a single photoelectric transducer receiving light fromall six of the lamps 5 through 10.

In a simple instrument having only a single keyboard, lamps 8 through10, photoelectric transducer 12, and circuit elements associatedtherewith, may be omitted. Conversely, if more than two keyboards aredesired, additional lamps and transducers may be provided using, ifnecessary, additional rotative discs carrying modulation tracks whichmay be identical to, or different from, the modulation tracks carried bydisc 1.

Within the broader aspects of this invention, the tone discs may bereplaced by other moving parts carrying endless modulation tracks, suchas rotating drums, endless loops of film, or the like; or rotating discsmay be used in arrangements other than thc parallel, coaxial arrangementherein specically described, and with optical systems other than thoseherein disclosed. Certain of the inventive principles herein disclosedand claimed, especially those principles relating to the production ofcomposite timbres from selected basic timbres and to the choice andarrangement of modulation tracks, are equally applicable tophotoelectric musical instruments having stationary tracks scanned bymoving light beams, such as those disclosed in my copending patentapplication entitled Moving-Beam Photoelectric Musical Instrument,Serial Number 543,948, tiled October 3l, 1955 and to other musicalinstruments not necessarily of the photoelectric type.

The light-modulating tracks carried by disc 1 are endless concentriccircular tracks which may each have a width of about one centimeter, sothat ten such tracks may conveniently be carried by a disc having aradius of about five inches. Modulated sections of the tracks have anoptical transmittance that varies along their lengths, and preferablyare of the variable-density type well known in sound-on-lm recording,although modulation tracks of other types such as variable-area tracksmay be used under certain circumstances. Variable density tracks arepreferred7 since with variable-area tracks distortion due topeak-clipping may occur during keying unless more elaborate keyingsystems are employed to uncover the entire width of a modulated sectionsimultaneously. Each track is generally modulated with a large integralnumber of wavelengths of the fundamental frequency. Preferably eachtrack is of the multi-section type described in my copending patentapplication entitled Progressively Keyed Electrical Musical Instrument,Serial Number 543,949, flied October 3l, 1955.

Various forms of shutters 13 and 15, and various means for linking theseshutters to the keys 14 and 16,

v' may be employed, as is more fully described in my copending patentapplication Serial Number 543,949 above identified. In a simple musicalinstrument, the shutters may be linked to the keys by direct mechanicalconnections. The apertures of shutters 13 and 15 are normally, in theunkeyed or rest positions of the shutters, in alinement with circularunmodulated sections of the modulation tracks carried by disc 1.Whenever either of the keys 14 and 16 is depressed, the apertures of theshutter linked thereto are moved into alinement with modulated sectionsof the modulation tracks so that a plurality of optical paths passingthrough respective ones ofthe modulated track sections are unblockedsimultaneously.

In a preferred arrangement of the tracks, all of the tracks upon any onedisc, such as disc 1, are modulated in accordance with various timbresof the same musical pitchthat is, all of the tracks carried by any onedisc represent musical tones having the same pitch or fundamentalfrequency, but having diterent timbres or harmonic contents. Forexample, one track may be modulated in accordance with the musical toneproduced by playing a selected note on a violin, while another trackcarried by the same disc may be modulated in accordance with the toneproduced by playing the same note on a trumpet, while a third track uponthe same disc may be modulated in accordance with the tone produced byplaying the same note on a tlute. Corresponding tracks carried by otherrotative discs are modulated in accordance with the musical tonesproduced by playing some other note on a violin, a trumpet, and a flute,respectively. Other instruments may be represented in the same way byadding additional modulation tracks, lamps, and associated parts.

Whenever either of the keys 14 and 16 is depressed, optical pathsthrough tracks modulated in accordance with violin, trumpet and llutetones of similar pitch are unblocked simultaneously. The relativeamplitudes of the violin, trumpet and flute tones produced when key 14is depressed are controlled by adjustment of selector switches 37, 38and 39. Similarly, the relative amplitude of the violin, trumpet andilute tones produced when key 16 is depressed are controlled byadjustment of selector switches 40, 41 and 42.

The total amount of modulated light reaching the transducer 11 or thetransducer 12 is the sum of the modulated light passing through theviolin, trumpet and ute modulation tracks, so that an additive tonesystem is provided for producing a signal having a composite timbresimilar to that produced when a violin, a trumpet and a ute are playedsimultaneously. Since the modulated sections of the tracks are modulatedin accordance with the tones produced by actual orchestral instruments,a very good simulation of orchestral music can be produced. By providinga sutcient number of modulation tracks, every instrument of a symphonyorchestra can be represented. If desired, non-orchestral instruments maybe represented by certain of the modulation tracks, and tracks may beprovided for producing tones that do not correspond to those of anypresently-known instrument.

To provide a separate modulation track for each pitch of everyinstrument represented in a large symphony orchestra would require theuse of a large number of: tracks, as well as a large number of lamps andother components. To reduce the number of tracks required, advantage maybe taken of the fact that the many instruments represented in a symphonyorchestra can be grouped into families of instruments having similarcharacteristics of tone color and the like, and differing from oneanother chietly in register. Consequently a very good simulation oforchestral music can be produced by an electrical musical instrument ofthe type herein described having a relatively small number oflight-modulating tracks, each of which is modulated in accordance with atone representative of a family of instruments.

In a preferred grouping of orchestral instruments in accordance withthis invention, the orchestral instruments essentie 9 Vvt'fhich'proiduceundampedttoralities are grouped'intogsix `families, as follows (1)vString family:

(a) Violins and violas (b) Cellos and double Vbasses (2.) Flute family:Flutes and piccolosr (/3) .Single reed family: Clarinets (-4.) Doublereed family:

(a) Oboes and English horns (.b) Bassoon (5 .Mellow brass family:.Frenchhorn (.6) Brilliant brass family:

(a) Trumpets and cornets (b) Trombones and tubas fAseventh family rkmayAbe 'addedfor .the tonality pro- 'duced by an organ diapason, but thisLtonality fcan be formed by rcombinations of Yother timbres, A.andconsequently it is not essential that separate modulation tracks'be-provided toproducer the organ Adiapason tonalrty..

By classifying orchestral instruments Vinto families as above described,and by Providing modulation `tracks `modulated .in accordance withtimbres representative ,of :each-family, allvof the undamped .tonalitiesof symphonic 'orchestral music can'be simulated Withzan electrical musi-:cal'instrument having only six modulation tracks per note.

vWith reference to the instrument illustrated .in Fig. 1, Fforexample,the innermost'track `carried by Vtone .disc .1 .may have .a sectionmodulated with a `tone 'color or Vtinibrerepresentative of the tintefamily, `themiddletrack may have a section modulated Withna tone colororvtimbre representative of the single reed family, and the outer- -mosttrack may.'have Vavtoue color for timbre representative-of thestring-family. Another similarinstrument, or 'additional tracks carriedby each Itone disc-'of the'same instrument, may simulate'the `doublereed, mellow'brass -and'brilliantbrass families.

In addition -to simplifying vthev construction fof Athe in- Lstrurnent,this classification lalso simpliiies'the rmusicians task in operatingVit,-sincestop settings are required only for whole families ofinstruments, rather than for vindiv'vi'dualinstruments.

If an `even 'better `simulation of lorchestral music -is desired, 4thestring, double reed, and brilliant brass famili'es'may each'be furthersub-divided .into two sub-families, as isindicated by .the4subparagraphs (a) -and Y(b) under each of these family classificationsinthe listing hereinbefore given. With this subdivision, "nine'modulation 'tracks per note areneeded to reproduce all of the undampedtonalities of an orchestra. Y

Other modulation tracks may be added, if desired, to represent thetonalities of the organ diapason and the .damped tonalities produced 'by the percussive finstruments such as the piano, harp, .kettle drum, andthe '.like, .as Well as the tonalities of non-.orchestral yinstrumentsand novel tonalities not produced by presently'known musicalinstruments.

Although principles of this invention may'be usedto construct anelectrical ,musical instrument capable of simulating van entireorchestra, it may in .some cases be Adesirable Vto construct electricalmusicalinstruments for simulating only "a single orchestral instrumentor 'amelatively small `group-of such instruments. 'For example, oneelectrical musical'instrument may be made to simu- Aflate all `of the-different orchestral instruments T'in Ythe string family, while anotherelectrical "musical instrument `may be made 'to simulate -all :of :theorchestral instru- :ments -in the Aute .and .reed families, tand yetanother electrical instrument may be made to simulate ithe .or-Vchestral .musical instruments inthe brass families.. Alvery'fewmusicians playing together might then produce Amusic.comparable to Athatproduced by fa :symphonic :orl-chestra `employing aYmuchlarger number .of musicians. .These .electrical musical nstruments.can besubstantially identical except for their modulation tracks, sothat a '110 musician can switch from 'one instrument to another, or canalter his instrument -vby substituting Ia different set of tonediscs'with no impairment of his `musicalproficiency. v

Modulation tracks may 'be provided to produce "tones similarfto thoseproduced by solo instruments, or tracks may -be provided for producingchoral effects or tonalitieslsimilar to those produced by manyinstruments play- 'ing the same note at the same time. If desired, (bothsolo and vchoral modulation tracks may be .provided in the samelelectrical `musical instrument. Alternatively, all of Vthe :modulationtracks :may represent solo instrujments. Similarly, modulation tracksmay be vprovided 'for lproducing tonalities `including 'vibrato or"tremolo effects, or'vibrato effects "andthe like may be produced bysignal 'modifiers connected Yin the circuit at'26.

Various vother 'arrangements of the modulation tracks are possible. Eorexample, tracks modulated Awith pure Asine-Wave tones 'may be providedYin which thetracks .on -each disciepresent 'different ipartials orharmonics ofa note. The innermost track, for example, could be sinewavemodulated at Ythe "fundamental frequency, while =ot`her tracks are.modulated in accordance with different Vovertones ofthe fundamentalfrequency. By adjusting 'the selectorsvvitches 37 *through 39 and 40through 42, 'any'desired'timbre'canthenibe formed bythe wellknown methodof 4harmonic synthesis.

Instead -of providing aseparate modulation track 'for 'each overtone,'groups of overtones may be combined on a single modulation track. In asmall instrument, *for example, three tracks 'may be used for eachpitch, in Awhich lthe inner track 'is .modulated at the fundamentalfrequency, Jthe Vnext track is modulated with a plurality Vof ,oddharmonicsof the fundamental, and the .third track Iismo'dulated with aplurality of even harmonics .of lthe fundamental. Althoughsuch a simpleinstrument would `notjs'imulate the tonalities of actual orchestralinstruments as faithfully as larger and more complex instruk'ey thetracks corresponding to lone pitch, while shutter 1`5'could bearranged'tolkey the ltracks corresponding .to theiother pitch. Keys 14and 1'6 would then be parts 'oftthe same'keyboard spaced .one octaveapart.

|Conversely, .in .a large instrument 'having more vbasic 'timbres vortonalities `of Veachjpitch than can conveniently fbeplaced upon asinglerotative disc, aplurality of .discs may be provided foreach pitch .andeach key.maybe Vlinked to aplurality of shutters associated with`different discs. Furthermore, extenders and couplers maybe .pro- -videdfor 'coupling together octavely relatcdkeys of the same keyboard, .orfor coupling togetherkeys of dilferent keyboards. In Vinstruments:having a large inumber of keyboards, including .manual keyboards .and`.pedal claviers, separate tone generators .may be .provided for eachvkeyboard or set .of keyboards .so that such -an.ins'trument isin'eifecta combination ofv several instruments -whichmay be `Aplayed from asingle.organ-type. console.

lven in vvery .large instruments, it may sometimes -be desirable toplace vtracks representing tones of vdifferent pitch upon thesame .tonedisc. For example, attone'disc Amay carrytracks .representing.instruments playing-.in different reg'isters-Aan octave apart, forexample. Exltendersani .couplers v.linking different keys together may"ibe ,.used1'for the samepurpose.

Reference is now made to Figs. 2 and 3, which show 1K1 a novellight-transmission circuit defining a plurality of optical paths fromeach of the lamps 5, 6 and 7 to the lphotoelectric transducer 11. Theoptical system shown in Figs. 2 and 3 provides twelve different pitchesthat preferably correspond to the twelve setnitones in an octave of theequal-tempered musical scale. Additional pitches may be provided byextending the optical system shown to include a larger number of tonediscs; by placing tracks representing a plurality of pitches on eachdisc; or by providing a plurality of optical systems similar to thatshown in Figs. 2 and 3, one such system being provided for each group ofpitches, which collectively cover a plurality of octaves. The instrumentcan be made in a variety of models of different size, ranging from smallportable instruments having a relatively small number of tone discs andone keyboard to large concert instruments having a large number of tonediscs and many keyboards.

Preferably one tone disc is provided for each pitch which is to beproduced by the instrument. To provide the twelve pitches needed in aone-octave instrument,

there are twelve tone discs, identified in the drawing by referencenumerals 1, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, and 53. The tonediscs are parallel and coaxial, and are rotated at different constantspeeds by driving means hereinafter described. Each of the tone discscarries a plurality of modulation tracks, as hereinbefore explained, thedifferent tracks on each disc being modulated in accordance withdifferent timbers or tone colors of the same pitch.

The three lamps 5, 6 and 7 are enclosed in three lamp housings, 54, 55,and 56. These housings communicate with three input light chambers 57,58, and 59, which are separated from one another by dividers 60 and 61,as is best shown in Fig. 3. The input light chambers 57, 58 and 59 arestacked in depth, as is best shown in Fig. 3, with a spacingcorresponding to the spacing of the modulation tracks on the tone discs.With tracks. one centimeter wide, vfor example, each of the input lightchambers is approximately one centimeter deep. Since lamps 5, 6 and 7ordinarily occupy a space greater than one centimeter in depth, the lamphousings 54, 55 and 56 `are somewhat larger than the depth of the inputlight chambers, and to accommodate this larger size of the lamp housingsthe housings are staggered in the manner shown in Fig. 2. If desired,curved mirrors may be placed in the rear portions of the lamp housingswhich focus the lamp filaments upon themselves.

The various parts of the input light chambers are supported by a frame62 having tongues extending parallel to the tone discs within alternateones of the spaces between the discs, as shown. Light produced by lamp 5is collimated by a mirror 63, which preferably is a segment of aparabolic cylinder with the filament of lamp 5 located at or near itsprincipal focus. In actual practice, however, a segment of a rightcircular cylinder or other approximation of the parabolic form may besatisfactory for mirror 63. In a similar manner, light from lamp 6 iscollimated by a mirror 64, and light produced by lamp 7 is collimated bya mirror 65. After leaving mirrors 63, 64 and 65, the collimated lighttravels in a direction substantially parallel to the common axis of thetone discs 1 and 43 through 53.

A plurality of distribution mirrors 66, 67, 68,69, 70 and 71 arepositioned in a stepwise staggered array, as shown, across and along thepath of the collimated light beams, and are or-iented at an anglesubstantially 45 to the direction of the collimated light so that aplurality of light beams are directed parallel to the tone discs withinalternate ones of the spaces between the discs.V

To facilitate manufacture and optical alinement of the distributionmirrors, these mirrors preferably are made as parts of a single integralstep-like member 72 having inclined risers which may be polished andsilvered to make reflecting surfaces. Alternatively, the distributionmirrors may be separate individual parts held in place by slots punchedin the dividers 60 and 61 and in the frame 62. The same distributionmirrors preferably extend through all three of the input light chambersand thus form similar parallel beams in each of the light chambertongues extending between the tone discs.

Mirror 66 directs a beam of collimated light parallel to and between thetone discs 1 and 43. A V-shaped beam-splitter mirror 73 positioned inthe path of this beam and between discs 1 and 43 splits the beam intotwo parts and directs one such part through a modulation track carriedby disc 1 and directs the other part through a modulation track carriedby disc 43. Preferably, the V-shaped mirror 73 also extends into allthree of the input light chambers, and it may consist of reflectingsurfaces on a metal inset that fits within the frame 62. Alternatively,mirror 73 may be supported by V-shaped slots in dividers 60 and 6l andframe 62. Frame 62 has exit apertures adjacent to the beam-splittermirrors to permit light to pass to the tone discs.

The beams directed through disc 1 are partially blocked by a keyingshutter 13, so that only those portions of the light beams that passthrough apertures of shutter 13 reach the modulation tracks of disc 1.Shutter 13 in its normal or rest positionV blocks the optical paththrough the modulated sections of the tracks, and permits light to passonly to unmodulated track sections.

VIn other words, in the rest position of a keying shutter,

its apertures are alined with unmodulated track sections, or,alternatively are alined with a mask to block the light beams.

When a key linked to shutterv 13 is depressed, the apertures of shutter13 are moved into alinement with modulated sections of the modulationtracks, and light thereupon passes through the tracks and is modulatedin accordance with the musical tones represented by the variations intransmittance of the modulation tracks.

In a similar way, light is directed along a plurality of optical pathspassing through each of the other tone discs and crossing respectiveones of the modulation tracks carried thereby. For this purpose, otherV-shaped mirrors 74, 75, 76, 77, 78 are positioned within alternate onesof 4the spaces between the tone discs in the manner shown. The pathsthrough the modulated track sections are normally blocked by keyingshutters 79,

v80, 81, 82, 83, 84, 35, 86, 87, 88 and 89, each of which is linked to adifferent key of the keyboard and each of which has a plurality ofapertures that become alined with and thus unblock the optical pathsthrough modulated track sections when the associated key is depressed.

After passing through the modulation tracks, light enters an outputlight chamber 90, which is generally similar to the input light chambers57, S8 and 59 except that the output light chamber does not havedividers corresponding to dividers 60 and 61 of the input lightchambers. Consequently, there is only one output chamber, and thischamber has a depth equal to the combined depth of the three input lightchambers. Light from from the modulation tracks enters entranceapertures in the frame 91 and is directed along a plurality of pathsparallel to the tone discs by a plurality of V- shaped mirrors 92, 93,94, 95 and 96 positioned withinother alternate ones of the spacesbetween the discs. The mirrors 97 and 98 at each end of the array oftone discs need be only half of a V, although V-shaped mirrors could beused in these positions for the purpose of reducing the number ofdifferent-shaped parts to be manu- A steplike member 99 provides aplurality of mirrors or reflecting surfaces 100, 101, 102, 103, 104, and106 which combine the beams coming from between the tone discs into abeam traveling substantially parallel to the common axis of the tonediscs. A condensing lens 'aantast r107 and a mirror 108 direct thislight to the cathode of photoelectric transducer 11.

As is best shown in Fig. 3, each of the tone discs, 'disc "46 forexample, carries a plurality of concentric circular modulation tracks109, 110 and 111 which are modulated in accordance with differenttimbres of similar pitch.

Th'einner portion of each circular modulation track is anvun'rnodulated, preferably opaque section, as is indicated by solidshading. Outer portions of each track, indicated 'dis'csaremodulatedwith somewhat `diiferent harmonic 'contents sothat the timbre or qualityof the tone produced varies somewhat from one pitch to another.Consequently, corresponding tracks represent similar timbres in thatthey simulate the same instrument orngroup of instruments, although thetimbres are not identical. This corresponds to the variations in tonecolor from note to note that'are found in conventional musicalinstruments;

`in consequence of which the electrical musical instru- Vmerit embodyingthe principles of the present invention `'simulates the tonalities ofother instruments more faithfully than can be accomplished withconventional priorart electric organs.

Illustrative Yexamples ofthe variations 'in harmonic vcontent Yas afunction of frequency encountered 'with 'orchestral instruments may befound, for example, on

"pages 216 through 230 of the book Musical Engineering by Harry F.Olson, lst'edition, McGraw-Hill Book Co., Inc., New York, 1952, andmeans are describedon pages '214 through 216 of the same book wherebythe frequency spectrum of Vany pitch of any instrument may be' obtained.vFor purposesof thepresent invention, how- "ever, analysis of thefrequency spectra is not necessary since the modulation tracks may bemade from recordings of different notes played on orchestralinstruments. The keying shutter 82 carries a plurality of opticalvz'rpertures'that normally are alined with unmodulated sections of thetracks carried by tone disc 46. These apertures 'are also alined withthe exit aperture in frame '262 through which light is directed towardthe tone disc. When a'key linked to shutter 82 is depressed, shutter 82'is moved upward, orradially outward with respect'to `"disc 446, and theapertures carried 'by the shutter are 'inove'd linto alinement withmodulated sections ofthe tone disc tracksv so that optical pathscrossing'aplurality 'of Vthe modulated track sections are unblockedsimul- 'taneou`sly. Consequently, when .a key'is depressed to 'movekeying shutter 82 upward, light passes through the 'modulated sectionsof tone disc 46 into the 'entranceslit v'ofthe output light chamber 90,whereupon modulated light reaches transducer 11 to produce an electricsignal corresponding to a desired musical tone. Chords maybe played inthe conventional manner by simultaneously 'depressing two or more keysof the same keyboard, or

vex'tende'rs may be used'for linking two or more keys together.

A plurality of similar optical systems, usually two f "such's'ystems,may be associated with one set ofjto'ne discs. The second optical systemincludes housings 112,

-1113' and`114 for the lamps 8, 9*, and 10 shown in Fig. v l.

`A` keying shutter 115 is linked to a key in the second keybard,'whichmay be either a second manual or a pedal i-clavier. When the key towhich it is linked is depressed, Lshutter "115 moves downward, .orradially-outward with lrespect to disc 46, to vbring its opticalapertures -into alinernent with modulated sections of the tracks carriedby tone disc 46'.

Selector switches 37 through 4-2 of the stop system can be adjusted sothat different 'cemposite timbres are pro- 14 Y 'duced when keys of theviirst and second keyboards, yrespectivelygare depressed.V Accordingly,themusician 'can Yset his stop system for two different compositetimbres, and can `'produce either of these timbres'at will by depressinga key in either the rst or the second 'keyboard, or both compositetimbres can be produced simultaneously to form a third composite timbreby simultaneously depressing keys in both keyboards. To hold the keying'shutters in their normal rest or inwardjposi- :tion when the keys arenot depressed, a small spring'11'6 Ymay be connected between the twokeying shutters .82 Vand'115, as shown.

To exclude dust and other foreign substances,the optica l systems `maybe enclosed and hermetically sealed. 15 Bellows or the like may beprovided to permit expansion yand contraction ofthe gas within thesystem. The .optical systems may be lledwith air or any othertransparent fluid. Alternatively, solid transparent i materialsinay'iill all or parts of the opticalsystems, as is'hereinlafter morefully explained.

The .instrument described is exceptionally rugged, can be lmanufacturedat reasonable cost, does not 'require `tuning, and requires a minimumamount of service and "maintenance Reference is now made to 'Fig 4,which is a 'detailof the keying shutter 82. In a preferredform, a keyingshutter includes an L-shaped metal supporting memberor 'frame which ispivotally supported on a shaft'117. The metal frame has a relativelylarge rectangular'ape'rture 118 which is covered byV a strip 119 ofphotographiclm 'or'.the like held .upon the metalfra'me bysuitablermeans such as rivets 120 and 121. Strip119 is generally opaque,but has a'plurality of small transparent areas "forming opticalapertures '122, '123 and 124- through which light passes tothe'modulationjtracks carried by the tone disc. This :arrangement ispreferable to having opticaljaperturesforme'd by cutting small holes intheshutter, vsince dust 'cannot enter the transparent apertures andconsequently thelight paths are less likely to be `obstructed 40`by dustor other foreign'substances. The transparent apertures may be madephotographically, by printing,'or by any other suitable method ofmanufacture. Alter- "na'tively, small holes lled with transparentplastic .may be used as optical apertures. In addition to the keying`shutter apertures, other optical apertures of the .instrument ycan bemade in a similar manner.

Reference now is made to Fig. 5, which shows lan alternative keyingshutter mechanism. The keyingshutter V125 vis rotative about the shaftZ'whichvsupports tone 59 disc v'46. A stationary mask 126 has a longnarrow aper- 'ture 127 preferably extending in a` direction radial tothe tone disc 46. Keying shutter 125 has a plurality of diagonalapertures 128, 129 and 130. Light passes through shutter 125 and mask126 only at the .points ywhere the keying shutter apertures are alinedwith the aperture 127 in the mask. In the normal rest or unkeyedposition ofshutter y125, the apertures 128,' 129,`r and 130 are eithercompletely out of alinement with aperture 127, Aor alternativelyonlyfthe lower ends of the keying g'shutter apertures are alined withthe mask aperture, so 'that' light is 'transmitted only to unmodulatedsections :of rthe modulation tracks carried by the tone disc. Shutter125 is linked to a playing key so that when the keyis depressed shutter12S moves counterclockwise -and vthus bringsha different portion of theapertures 128,129 and 130 into alinement 'with aperture 127. 'This isequiva- Ylenttonioving a Vsmall kaperture in thetradi'al direction withrespect to disc teY in the manner of keying shutter 82, and permitslight to cross modulated sections of the tone disc tracks.

""Fig. 6 is a detail diametric section showing a preferred constructionof a tone disc. A transparent disc V131 may b emade ofglass or othertransparent material-such as 'Mylar,"polystyrene, or cellulose acetate.A.Disc -131f'is secured to a hub 132 which may be made of metal, nylon'wheel for each tone disc.

diameter, are driven at different constant speeds.

or other suitable material, by a plurality of rivets 132. Hub 132 isfreely rotative on the metal shaft 2 which supports all of the Vtonediscs. The modulation tracks are printed or are formed photographicallyon a film 133 carried by the disc 131. If desired, instead of using afilm 133, a photographic emulsion may ne coated directly upon thesurface of disc 131. To inhibit shrinkage, buckling and other damage tothe film 133, it may be covered by a coating 134 of cellulose acetate orother suitable material, preferably applied as a liquid and drying to ahard transparent solid. Hub 132 may be made sufficiently long to contactthe opposite end f the hub of the next adjacent tone disc for thepurpose of keeping the discs in the desired axially-spaced relation.Alternatively, the disc hubs may be somewhat shorter, and spacers,bearing supports, or other means may be used to position the discs onshaft 2.

The modulation tracks carried by film 133 preferably are photographicreproductions of a master tone disc which may be made, for example,using sound-on-film recording techniques, from recordings of tonesplayed on the orchestral instruments that are to be simulated. Once aset of master tone discs has been prepared, reproductions in largequantities may be made at little expense for the economical massproduction of electrical musical instruments embodying principles of thepresent invention. Alternatively, photoengraving techniques may beemployed for making printed reproductions of the master tone discs, orother methods of tone disc manufacture may be used.

Reference is now made to Figs. 7 and 8 which shows a preferred drivingmechanism for rotating the tone discs. The tone discs 1 and 43 through53 are coaxial and axially spaced apart as hereinbefore explained.average spacing between discs is preferably 0.55 inch,

.which corresponds to the average spacing between keys on a conventionalpiano or organ-type keyboard. In actual practice, some of the discs arespaced somewhat closer together than the average spacing, while othersare spaced somewhat farther apart, to accommodate the optical systemshown in Fig. 2 more conveniently.

A motor 3 is linked te a drive shaft 1%' and rotates shaft 135 at aconstant speed. Shaft 135 carries a plurality of driving wheels 4, 136,137, 13S, 139, 140, 141, 142, 143, 144, 145 and 146, there being onedriving Each of the driving Wheels is of a slightly different diameterfrom the others so that the tone discs, which preferably are all of thesame Preferably, the diameter of one driving wheel is related to that ofthe next adjacent driving wheel by a factor equal to the twelfth root oftwo, which corresponds to the frequency spacing between adjacentsemitones in the equaltempered musical scale. It will be understood thattones of different pitches-for example, tones spaced one or more octavesapart--can be generated by tone discs rotated at equal speeds, buthaving tracks modulated with different, integral numbers of wavelengths.

The driving wheels are connected to the tone discs by a plurality ofidler wheels, represented by reference numerals 147 through 158, whichfrictionally engage the driving wheels and the tone discs. Since theratio of a tone disc speed to the speed of shaft 135 depends only uponthe relative diameters of the tone disc and the associated drivingwheel,and not upon the diameter `of the idler wheel, so long as it iscircular, the materials used are so chosen that most of the wear thatoccurs during operation of the instrument is upon the idler wheelsrather than upon the driving wheels and the tone discs. The tone discsmay be glass or a hard transparent plastic, and the driving wheels maybe steel or other hard metal. The rimsof the idler wheels may`advantageously be covered Ywith rubber or some other elastomer.

Each idler wheel is supported by arms loosely pivoted on a rod 159.Idler wheel 158, for example, is supported The' by a pair of arms 160and 151 having slots as indicated at 162, Fig. 8, through which rod 159passes. A spring 163 urges arm 16d downward to bring idler wheel 158into firm frictional engagement with driving wheel 146 and into lightfrictional engagement with tone disc 53. Shaft rotates in the directionindicated by arrow 164, so that rotation of the driving wheel also urgesidler wheel 158 into engagement with the tone disc. However, thearrangement is such that idler 158 exerts only a small amount of forceagainst tone disc 53, so that there is negligible tendency for the tonedisc to bend or buckle.

Various changes and modifications can be made in the driving mechanism,including the use of gears and the like in place cf frictionally engagedwheels. Frictionally engaged wheels have an advantage, however, indamping oscillations excited by fluctuations and vibrations in thedriving mechanism. Modification can also be made inV other parts of theinstrument, and in particular with respect to the light chambers andoptical systems. For example, a row of partially-reflecting mirrorsmight replace the stop-like array of distribution mirrors. If desired,the optical system shown in Figs. 2 and 3 may be enclosed in anhermetically sealed container, and may be filled with some othertransparent uid in place of air. Such sealing is especially advantageousin excluding dust, moisture and other substances that might affect theoptics adversely.

Alternatively, solid transparent light-transmitting materials may beused in the light chambers in place of uid fillings. For example, thelight chambers shown in Figs. 2 and 3 may be completely filled with atransparent solid, as is illustrated in Fig. 9, for example, and themirrors of the optical system may be reflecting surfaces formed on suchsolid material. The mirrors may be formed by polishing and silvering thedesired surfaces of the solid light-transmitting material, or unsilveredsurfaces may be employed with materials having a high refractive indexsuch that substantially complete internal reflection occurs in rayshaving an angle of incidence to the surface of substantially 45. The useof solid transparent materials for the light chambers has the advantagethat such material may be cast or otherwise formed into the desiredshape, and thereafter very little optical alinement is necessary in theassembly of the optical parts.

In Fig. 9, parts that are identical to parts shown in Fig. 2 areidentified by the same reference numbers; and parts that are somewhatdifferent in form but similar in function to parts shown in Fig. 2 areidentified by the same reference numbers with a prime added. The threeinput light chambers are three comb-like transparent solid members 57',58 and 59', which are preferably made of pure cast methyl methacrylateor an equivalent light-transmitting solid material having a highrefractive index. Curved surfaces 63', 64 and 65 at the lefthand ends ofmembers 57', 58 and 59 are silvered to form collimating mirrors thatperform the same functions as mirrors 57, 58 and 59 of the embodimentshown in Fig. 2. Oblique surfaces 66 through 71 in the base of members57', 58' and 59 serve as distribution mirrors to direct light beamsalong teeth or tongues of members 57', 58 and 59 extending between andparallel to the tone discs 1 and 43 through 53, as shown. Surfaces 66through 71' are not necessarily silvered, since the angle of incidenceof the collimated light to such surfaces, which is substantiallyforty-tive degrees, exceeds the critical angle for amethyl-methacrylate-air boundary, in consequence of which total internalreflection of the light occurs. The inner ends 73' through 78 yof theteeth or tongues of members 57', 5S and 59' are V-shaped, as shown, toform surfaces at which the light is again reflected internally, so thatthe light beam transmitted down each tooth is split into two parts whichare directed toward adjacent ones of the tone discs. After the beams i7are split, they pass through the sides or" the' solid lighttransmittingteeth substantially perpendicular thereto.

The output light chamber is a comb-like transparent solid member 90',preferably made of methylmetliacrylate, having teeth or tongues whichreceive the light transmitted by the tone discs. Inner ends 92 through98 of these teeth have inclined 'surfaces which reflect the light' alongthe teeth to oblique surfaces 160 through 106' in the base of member90', which again reiiect the light through a condensing system tophotoelectric transducer 11. The right-hand end 107 of member 9d iscurved to form a condensing lens that performs the` saine functions aslens 107 of the embodiment illustrated in Fig. 2. The light-transmittingmembers 57', 5S', 59", and 90 are supported by frame members, net shown,and the three input light-transmitting members are separated by opaquedividers.

Instead of filling the entire light chamber with transparent solidmaterial, light pipes made of such material as pure castmethylmethacrylate may be employed. Such pipes may be bent to transmitlight around corners and thus eliminate at least some of the mirrorsfrom the optical system.

Figs. l and ll illustratekan alternative optical system using bothgasalled chambers and solid transparent members for transmitting thelight. Only iive tone discs are shown, but it will be understood thatany desired number of such discs may be provided, and that more than ivetone discs will generally be provided, duplicate optical parts beinginserted between the broken-oil sections shown in Fig'. l0. Partsidentical to these in the embodiments hereinbefore described areidentified by the same reference numbers.

In this alternative optical system, the three lamps 5, 6 and 7 of Fig. lare replaced by a single lamp 165 of an elongated type, such as afluorescent or other gaseous conductor which provides an elongated lightsource hav-l ing a length greater than the distance between the rst andlast of the parallel light beams entering the spaces between the tonediscs. Elongated light sources of other types may be used, such asincandescent lamps placed behind a diffusing plate. Lamp 165 may beoperated at constant brightness, or its brightness can be varied bymeans linked to the swell pedal for controlling the overall loudness ofthe composite musical tone produced by the instrument.

As shown in Fig. l0, lamp 165 is contained in the upper portion of anelongated input light chamber 166, having its lower portion divided intothree sections by dividers 167 and 1.67', as Iis best shown in Fig. 1l.Solid transparent rods or light pipes extend from input chamber 166parallel to the tone discs `1, 43, 44, 45 and 46, vbetween alternateones of the spaces :between the discs, as shown. The threelight-transmitting rods .168, 169 and 170 are alined .with the.outermost modulation tracks carried by the tone discs. Immediatelybelowthese three light-transmitting rods there are three similar rods 171,172 and 173, the inner ends of which are alined with the middlemodulation tracks carried by the tone discs. Immediately below :theserods is `a third set of light-transmitting rods 174, 175 and 176 havingtheir inner ends aligned with the innermost modulation tracks carried bythe tone discs.

The outer ends of these nine light-transmitting rods are illuminated bylamp 165 through apertures carried by a plurality of adjustable slidingmasks y177, 178 and 179, as shown, which are parts of a stop system forcontrolling the composite timbre of the musical tone produced by theinstrument. Each of these masks has a plurality of tapered apertures, asis best shown in Fig. ll, alined with respective ones of thelight-transmitting rods. By moving each mask, the relative amounts oflight transmitted to the outermost, middle, and innermost modulationtracks can ybe adjusted.. Instead of tapered apertures, optical wedgesor Ithe like may be carried by masks 1'77,

gallegas nits 178 and 179 for adjusting the relative amounts of lightsupplied to .the three sets of light-transmitting rods.

Each of the light-transmitting rods l168 through 176 has a V-shapedinner end which may be silvered to form a V-shaped .beam-splitter mirroror reflecting sur- `face which directs light through the tone discs in amanner similar to the operation of the V-shaped beam-splitter mirrorsshown in Fig. 2. After passing through the tone discs, light entersanother set `of light transmitting rods 180, 181 and .182 which aregenerally similar .torv the light-input rods 168 through 176, exceptthat each of rods 189, t151 and 132 has a depth equal `to the overa. allradial distance occupied by the modulation tracks. Rods 180, 181 and 182transmitthe light to an output light chamber containing mirrors 183, 184and l85rtwhich direct the light through a .collecting lens 186 to .thecatliode of photoelectric transducer 11.

Since the light directed through the .tone disc tracks may not be wellcOIlimated, to provide a satisfactorily small elective aperture for themodulation system' the keying shutters may be modiied in the followingmanner:` Keying shutter part 13, for example, maybe identical to thekeying shutter'13 described in connection with Fig. 2, .but linkedthereto and on the other side of tone disc 1 there is a similar lkeyingshutter part 13 having a plurality of optical apertures that are alignedwith the apertures of shutter part 13. Shutter part 13 is linked toshutter par-t 13` by a connection 1-87 so that these two parts of thekeying shutter move together. Of the light that is directed through tonedisc 1, the only portion that reaches the output light chamber is thatwhich passes through the apertures of both shutter parts 13 and 13', sothat the ellective aperture with respect to the modulation trackscarried by -disc 1 is the small and well-defined path that is alinedwith the apertures of .both shutter parts. In a vsimilar way, keyingshutter .part 79 has associated therewith another shutter part '79 .upon.the opposite side of tone disc 43, shutter part has a second shutterpart Su', shut-ter part 81 has a second shutter part 81', and shutterpart 32 has a second shutter part 82'.

Still another alternative optical system is shown in Fig. l2. In thisembodiment, in which parts identical to parts of embodimentshereinbefore described are identiled by the same reference numbers, thelamp 5 and the mirror 63 produce a collimated .beam of ylight traveling.parallel to the axis of the tone discs, which are identical .to thetone discs hereinbefore described and hence are not shown in Fig. l2.Extending into alternate ones 'of :the spaces between the tone discs area plurality of light-transmitting solid transparent rods l188, 189 and190, wh-ich have V-shaped rellecting surfaces at their inner ends -for`directing light wthrough the modulation tracks carried by the tonediscs. The .outer ends of rods v188, 189 and 190 extend forprogressively greater distances into the input light chamber 191, sothat each rod intercepts substantially the same amount of light `fromthe col.

limated beam produced by lamp 5 and mirror 63. These outer ends yof rods188, .189 and 190 have oblique reecting surfaces so that light receivedAfrom the coll-imated beam is retlected along the length of thelight-transmitting 'rods parallel to and ibetween the tone discs.

A similar system is used .to collect the light that passes through themodulation tracks. Transparent solid rods 192, 193 and 194 have at theirinner ends V-shaped (or halt V-shaped) reflecting surfaces j whichdirect light from the tone discs along the lengths of rods '192, 193 and194 parallel to the discs Within alternate ones of the spaces betweenthe discs. The output light rods 192 through 194 extend forprogressively decreasing distances into the output light chamber 195,and the outer ends of :these rods have oblique rellecting surfaces whichdirect the light down `the length of. the output light chambersubstantially parallel to the axis of the .tone discs. -A collectingmirror 196 directs this light to the cathode of photoelectric transducer11. i

In all of the embodiments described, various permutations in the orderor positions of elements of the optical Systems may be made. Forexample, the keying shutters Vmay be placed on either side of the tonediscs, and the positions of light sources and photoelectric .transducersmay he transposed so that light -travels through the optical systems inthe reverse direction to that described.

It'should be understood that this invention in its broadcr aspects isnot limited to specific embodiments herein illustrated and described,and that the following claims are intended to cover all changes andmodifications that do not depart from the true spirit and scope of theinvention.

What'is claimed is:

n l. An electrical musical -instrument comprising at least one uniformlymovable uniplanar member having an optical transmittance sound recordthereon, a source of light having a beam substantially normal to theplane of said member, a first reflector spaced from said member,slightly offset from .the plane thereof and in line with said beam, asecond reflector adjacent said member and in line with said rstreflector, a third reflector adjacent said member and on the oppositeside thereof from said second reflector, a fourth reflector in line withsaid third reflector, and a photoelectric transducer in line with saidVfourth reflector.

2. An electrical musical instrument comprising at least two uniformlyrotative parallel discs, each of said discs having an opticaltransmittance sound record thereon, a source of light having a beam ofcollimated rays substantially normal to the parallel planes of saiddiscs, a first reflector spaced from a `first one of said -discsslightly ofsetrfrom the plane thereof and in line with said beam, asecond reflector adjacent to said first disc and in line with saidyfirst reflector, a third reflector adjacent to said first disc and onthe opposite side thereof from the second reflector, a fourth reflectorspaced from said first disc and in line with said third reflector, afifth reflector spaced from a second one of said discs slightly offsetfrom the plane thereof and in line with said beam, said first and fifthreflectors being yin a stepwise arrangement relative to said beam, asixth reflector adjacent to said second disc and in line with said fifthreflector, a seventh reflector adjacent to said second disc and on theopposite side thereofA from said seventh reflector, an eighth reflectorspaced from said second disc and in line with said seventh reflector,all of said eight reflectors being positioned in planes at 45 angles tothe parallel planes of said rotative discs, a light collector in linewith both of said fourth and eighth reflectors, said fourth and eighthreflectors being -in stepwise arrangement relative to said lightcollector, and a photoelectric transducer in line with said lightcollector.

' 3. In an electrical musical instrument, the one-note, multi-timbre,tone-generating subcombination comprising a plurality of electric lamps,a photoelectric transducer producing electric signals responsive tomodulated light, an optical transmission system defining a plurality oflight-beam paths each extending from a different one of said lamps tosaid transducer, a support having thereon a plurality of modulationtracks each crossing a differenht one of said paths, each of saidmodulation tracks having an optical transmittance that varies along itslength, the transmittance of said tracks being modulated in accordancewith complex musical tones of the same pitch in all of said tracks anddifferent timbres in different tracks, means moving said tracks relativeto said paths in a direction lengthwise with respect to the tracks andtransverse with respect to the paths `for modulating the light in saidpaths, a note-playing keyboard key, a unitary keying shutter normallyblocking and operable by said key to unblock a plurality of said pathssimultaneously for producing a composite musical tone, circuit means for.supplying electric current to said lamps, and separate adjustmentmeans, one for each lamp, for adjusting the amount of current to eachindividual one of said lamps for controlling the timbre of saidcomposite tone.

4. In an electrical musical instrument, theone-note, multi-timbre,tone-generating subcombination comprising a plurality of electric lamps,a photoelectric transducer producing electric signals responsive tomodulated light, an optical transmission system defining a plurality oflight-beam paths each extending from a different one of said lamps tosaid transducer, a rotative member carrying a plurality of circularmodulation tracks, each of said tracks crossing a different one of saidpaths, each of said modulation tracks having an optical transmittancethat varies along its length, the transmittance of said tracks beingmodulated in accordance with musical tones of the same pitch in all ofsaid tracks and of different timbres in different tracks, means rotatingsaid member continuously at a constant speed for modulating the light insaid paths periodically in accordance with said tones, a unitary keyingshutter adjacent to said tracks and normally blocking a plurality ofsaid paths, a ykeyboard key linked to said shutter and operable to movesaid shutter and simultaneously unblock a plurality of said paths forproducing a composite musical tone, a plurality of current distributionlines, means supplying each of said lines with a different voltage, andswitching means for connecting each individual one of said lamps to anyselected one of said distribution lines for controlling the relativebrightnesses of said lamps.

5. An electrical musical instrument comprising a plurality of memberseach carrying a plurality of light-modulating sound tracks representingcomplex musical tones, all tracks carried by the same one of saidmembers being representative of the same note with different timbresrepresented in different tracks, corresponding tracks on `different onesof said members being representative of different notes of similartimbre, a plurality of multibeam light sources, each of said sourceshaving different beams directed to the corresponding tracks carried bydifferent ones of said members, the beams from different ones of saidsources being directed to different tracks on each member, said membersand said beams being relatively movable longitudinally of said tracksfor modulating the light of said beams in accordance with said musicaltones, a photoelectric transducer optically alined with said tracks forreceiving the modulated light transmitted thereby, a plurality ofnote-playing unitary shutters each adjacent to a different one of saidmembers and normally blocking said light beams directed to that member,each of said shutters being individually operable to unblocksimultaneously said light beams directed to that adjacent member forproducing a complex musical tone representative of a selected note and acomposite timbre, and a plurality of individual adjustment devices, onefor each of said light sources, for adjusting the relative brightnessesof said light sources to controllably vary said timbre. 6. An electricalmusical instrument comprising a plurality of parallel coaxialspaced-apart rotative discs, each of said discs carrying a track havingan optical transmittance that is modulated in accordance with a musicaltone, a lamp producing light, means directing said light -in acollimated beam parallel to the axis of said discs, a plurality ofmirrors positioned in a stepwise staggered array across and along saidcollimated beam to produce a plurality of spaced-apart parallel beamspassing parallel. to said discs within alternate ones of the spacesbetween said discs, a plurality of V-shaped mirrors positioned in saidparallel beams within said alternate spaces to split each of such beamsinto two parts passing in opposite directions through tracks on adjacentones of said discs, another plurality of V-shaped mirrors positionedwithin other alternate ones of said spaces for directing the lighttransmitted by said tracks in other parallel beams passing parallel toand between said discs,

21 means including another plurality of mirrors arranged in a stepwisearray for collecting the light from said other parallel beams, and aphotoelectric transducer receiving the collected light.

References Cited in the file of this patent UNITED STATES PATENTS 22Ranger Feb. 19, 1935 Kucher Apr. 23, 11935 Eremeei Feb. 11, 1936 DavisApr. 6, 1937 Kannenberg Aug. 15, 1939 Land et al. May 22, 1945 SpielmanOct. 18, 1949 Grudin Ian. 23, 1951 Phillips Feb. 6, 1951 Knoblaugh etal. Oct. 16, 1951 Knoblaugh Feb. 19, 1952 Williams Mar. 11, 1952

